The designs of most wheelchairs are optimized to accommodate a particular level of disability. Persons with low disability tend to use wheelchairs that have no seat tilt or a fixed seat tilt and a footrest assembly that easily accommodates self-propulsion using the occupant's feet.
Persons with moderate disability may prefer a wheelchair that allows for optional self-propulsion but that can be tilted to offer a range of seating angles. Tilting the seat provides pressure relief to the occupant, reduces discomfort associated with sitting for long periods of time, and provides passive correction for deformities. The ability to self propel using the feet may be preserved despite various tilt angles by providing the axis of rotation near the front of the seat such that the distance from the knees to the ground remains relatively constant. A disadvantage of such a configuration is the force required in order to move the weight of the occupant about the axis of rotation. This is sometimes compensated for by a pneumatic assist mechanism extending between the base of the chair and the seat frame as described in commonly owned U.S. Pat. No. 6,447,064.
High disability individuals typically require a wheelchair with deeper tilt angles to improve trunk stability and head control. Some such wheelchairs also use mechanical actuators to accommodate the significant force sometimes required to move the weight of the occupant through deep tilt angles. It is also known in the prior art to minimize the effort required to tilt the occupant by providing a pivot point as close as possible to his center of gravity. U.S. Pat. No. 7,007,965 provides an example of such a system.
While various tilt configurations may be suited to particular types or levels of disability, many individuals suffer from disabilities that progress over time. Over the course of such a disability, the occupant may graduate through 3-4 different types of wheelchairs, each having different attributes. For example, a no-tilt or fixed tilt wheelchair may be used at the early onset of disability, a self-propellable tilting wheelchair can be used when the disability becomes moderate, and a deep tilt wheelchair can be used in the later stages of disability.
The present invention addresses the need for a reconfigurable modular wheelchair that is capable of being selectively configured in a fixed tilt configuration, a dynamic tilt-in-space configuration with the axis of rotation near the occupant's knees, or a dynamic tilt-in-space configuration with the axis of rotation near the occupant's center of gravity, as required to accommodate the evolving needs of the occupant.